John & Johnnydajewler are totally correct & almost totally correct, respectively. It is a Snake River Fine-Spotted Cutthroat. This image is the first I ever fooled on a recent trip to the Sun Valley during late September.

Specifically, it is from the junction pool of the East Fork of the Lost River & Wildhorse Creek in the Copper Basin east of Sun Valley Idaho. It ate a #16 Rubber-Legged, Purple Copper John...on my first indicator/nymphing presentation into the pool. 5-6 cast later I hooked a second one of almost identical size.

I may post some images...it was a quickie 6 day driven trip at 4 different venue. Had fun seeing some new turf & fly fishing waters; although it has been eons since my last fly angling at Silver Creek.